It could be really interesting. Saitama is extremely powerful in his own universe, and in a Dragon Ball Super fanfiction, he might be a wild card. Maybe he'd show up during a big tournament and shock all the Saiyans with his effortless strength. His simple, unassuming personality would contrast with the more flamboyant Dragon Ball characters.
Dragon Ball Super vs GT in fanfiction can lead to some really interesting character developments. The different timelines and power systems in both series offer a lot of room for creativity. In some fanfictions, the younger characters from Super might meet their older counterparts from GT. This can create a contrast in personalities and fighting styles. For example, Trunks in Super is more used to the modern power-ups and technology, while Trunks in GT has a more 'old - school' approach. Fanfic authors often use these differences to create engaging stories that explore not only the battles between the two series but also the underlying themes and character growth.
I think Saitama is stronger. His power is seemingly limitless and he has never struggled in a fight. Goku, although powerful, has had many intense battles where he was pushed to his limits.
In my opinion, Saitama doesn't have a chance against Goku. Goku has mastered multiple forms of Super Saiyan and has fought incredibly powerful foes across multiple universes. Saitama's strength is impressive, but it's not on the same level as Goku's.
It's really hard to say. Goku has his Super Saiyan forms which give him incredible power boosts. But Superman has super strength, heat vision, and is nearly invulnerable. In a short fight, Superman might have the edge due to his instant powers like flight and super strength without having to power up. But if Goku manages to reach his higher Super Saiyan forms and uses techniques like the Spirit Bomb, he could potentially defeat Superman.
Another theme could be the clash of different universes. Amazo is from the DC universe and Saitama is from One Punch Man. Fanfics might play around with how these two different universes' rules and powers interact when these two characters meet. Also, there could be themes related to respect and rivalry. Saitama is often very nonchalant about his power, while Amazo is a complex android with various abilities. How they view each other in the fanfic can create interesting storylines.
It's hard to say. Goku in Dragon Ball Super has Ultra Instinct which gives him incredible speed and reflexes. But in GT, his Super Saiyan 4 form is also extremely powerful. However, if we consider the fact that Ultra Instinct seems to be a more refined and spiritual form of power, it might give Goku in Super an edge. But then again, the Super Saiyan 4 form has its own advantages like the combination of Saiyan and Great Ape power.
Another possible ending is that Gohan sacrifices himself to defeat Cell. He could use a self - destructive move that not only takes out Cell but also costs Gohan his life. This would be a very dramatic and tragic ending, but it would also show Gohan's selfless heroism.
Maybe a story where the Dragon Balls are accidentally sent to the DC universe. This would attract the attention of characters like Batman who would be intrigued by their power. Then, characters from Dragon Ball would have to travel there to retrieve them, leading to all sorts of encounters and battles.